In-line control of nonlinear pH neutralization based on fuzzy logic

pH control is important to semiconductor manufacturing, with some common applications including etching, acid treating, and wastewater neutralization. In particular, pH neutralization is notorious for its severe process nonlinearity, which is reflected in the titration curve and shows process gain change of up to 10000 to 1 over a very small region. In this paper, we describe a new technique of in-line control of pH neutralization based on fuzzy logic. The unique features of this fuzzy control technique include 1) a wider operation range for handling a nonlinear process, 2) robustness for dealing with random disturbances and possible system parameter drafting, and 3) relatively simple implementation. Laboratory experiments are performed demonstrating that the controller works well over a wide operational range